Field of the Invention
The present invention relates to an image forming device and a method for correcting a scanning position of a luminous flux.
Description of the Related Art
An electrophotographic image forming device generally forms a latent image of an image on one page by deflecting a laser beam, which has been modulated based on original image data, by a polygon mirror and repeatedly scanning on a rotating photoreceptor in a main scanning direction. An image can be formed on paper by transferring, on the paper via an image carrier such as an intermediate transfer belt, an image which has been developed by feeding a color material such as toner on the photoreceptor, on which the latent image has been formed.
In a case where an image is formed by superimposing images of a plurality of colors, in order to adjust a position of the image of each color, timing for initiating scanning by the polygon mirror in the main scanning direction is synchronized with timing for initiating scanning by rotation of the photoreceptor in a sub scanning direction (for example, see JP 2000-103115 A).
However, even when a first scanning position is synchronized, a scanning position of a luminous flux in a main scanning direction may change due to unevenness, for example, of mirror surfaces of a polygon mirror and cause deviation of an image position within one scanning line. The scanning position in a sub scanning direction may also deviate depending on characteristics of the mirror.
Such a deviation of the scanning position, attributable to the polygon mirror, may be repeated with a rotational period of the polygon mirror and observed as a density fluctuation.
In particular, like a screen pattern, for example, where dots are arranged regularly, an image having a periodic pattern is likely to generate the density fluctuation called moire by a periodic deviation of a scanning position.